Make protected tags available only when using the new registry

What does this MR do and why?

Make protected tags available only when using the new registry

Use injected value to show/hide protected tag settings

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• https://gitlab.com/gitlab-org/gitlab/-/issues/499871+
• #506402+
• MR which added the is_container_registry_metadata_database_enabled attribute Add metadata database alert to registry pages i... (!147503 - merged)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

N/A

How to set up and validate locally

1. Setup & enable Container Registry https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/registry.md

2. Enable feature flag

   Feature.enable(:container_registry_protected_tags)

3. Visit Project > Settings > Packages and registries.

4. Expand Container registry section

5. Confirm Protected container tags section is hidden.

6. Enable the metadata database https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/registry.md#metadata-database

7. Reload the page & confirm Protected container tags section is visible.

Related to #506402